Recording titration apparatus



1954 H. A. ROBINSON ETAL 2,666,691

RECORDING TITRATION APPARATUS Filed Oct. 13, 1948 5 Sheets-Sheet 1 r i a 25 4 27 7%;? Q inn 26 5AA Q5 66A 85A '99, 5

. 37 r ADI (Q, @J I 42 L R 9M IrvueNToraJ 20 Harold CLRobinSOH RollLn Hbriggs 8;; A 3, mu... Q. 4..

3% n 2 L 3 U( v m, w. h mmw EDGE TU )(JMH PSQQU munzmm Jan. 19, 1954 Filed Oct. 13, 1948 1954 H. A. ROBINSON ETAL RECORDING TITRATION APPARATUS 5 Sheets-Sheet 3 Filed Oct. 13, 1948 INuBNToRAr Harold a. Robinson Rollin H. B21996 1954 H. A. ROBINSON ET AL 2,666,691

RECORDING TITRATION APPARATUS Filed Oct. 13, 1948 5 Sheets-Sheet 5 A 4| II||lllllllll llll lflllllwlI ll lllllll ly ifl ISO

' *SA- 46 166 \76 |S6 48 M69 we, INVENTOR/J Harold (1. Robinson Rollin H. 511935 Patented Jan. 19, 1954 UNITED STATES ATENT OFFICE RECORDING TITRATION APPARATUS ware Application October 13, 1948, Serial No. 54,304

3 Claims.

The present invention relates to devices for performing titrations.

It is an object of the invention to provide a novel apparatus for determining by electromotive force measurements the acidic or basic strength of solutions of unknown concentration, which is operative both to perform a titration and to record the electromotive force measurements directly in the form of a plot or titration curve.

Another object resides in the provision of titration apparatus which is effectual in its operation to automatically perform a titration and to simultaneously record a titration curve, novel means being provided to keep the recorder pen and titrator in step for the production of an accurate record.

It is a more specific object to provide an automatic titrator with provision for synchronizing movement of the recorder chart with the addition of reagent standard solution.

The objects of the invention thus generally set forth together with other and ancillary advantages are attained by the construction and arrangement shown by way of illustration in the accompanying drawings, in which:

Figure 1 is a perspective view of a titration apparatus embodying the features of the present invention.

Fig. 2 is a block diagram illustrating the general arrangement of the instant device.

Fig. 3 is a schematic circuit diagram o'f'the bridge circuit.

Fig. 4 is a schematic circuit diagram of the recording instrument.

Fig. 5 is a schematic circuit diagram of the relay circuit.

Fig. 6 is a fragmentary elevation of the chart and syringe feed mechanism.

Fig. 7 is a fragmentary plan view of the chart and syringe feed mechanism.

While the invention is susceptible of various modifications and alternative constructions, there is shown in the drawings and will herein be described in detail the preferred embodiment, but it is to be understood that it is not thereby intended to limit the invention to the form disclosed, but it is intended to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

A titration is a volumetric determination of the strength of an acid, base, or the like, and is per formed by the addition of .a solution from a graduated container to a known volume of a sec ond solution until a neutralization reaction between the two is completed. Ordinarily, the added solution is one of known concentration or strength and thus constitutes a standard, and the second solution is the one of unknown strength. From a knowledge of the volume of solution added and its strength and the original volume of the solution of unknown strength, one can readily calculate the strength of the unknown solution. In other words, the purpose of any type titration is to determine what volume of one solution is equivalent to a certain volume of another solution, or to determine an equivalence point.

Some means must be utilized to notify the chemist performing the titration when the equivalence point is reached. Commonly, certain organic substances whose color changes at or near equivalence point are used. However, such indicators do not always change color at the same point, and further in titrations of solutions which are themselves colored or are turbid, ordinary color indicators are useless. Such titrations may be accomplished by'inean's of electromotive force measurements in a chemical cell involving the solution of unknown strength, since near the equivalence point in a titration the hydrogen ion concentration changes rapidly, and correspond ingly, there is a rapid change in electroinotive force output from the cell. Thus, a plot of the electromotive force against the volume of stand ard solution added, which is known as a titration curve, will show the point where the hydrogen ion concentration changes most rapidly, such point being the equivalence point.

To obtain electromotive force readings for plotting, two electrodes one of which may be a neutral or glass electrode and the other a calomel electrode, are suspended in a known volume of the solution of unknown strength and to which a standard solution is slowly added, the volume thereof being measured. These electrodes are connected to some form of electromotive force indicating instrument such, for example, as a galvanometer. The change in E. M. F., or voltage, between the electrodes as indicated by the measuring instrument during the titration is exactly equal to the change of potential of the neutral indicator electrode. A calomel electrode is preferred for the other half of the chemical cell because it is a definite standard and is reproducable in any laboratory without any assumption regarding ionization. It is rugged, changes little, is convenient to handle and has a substantially constant potential.

In determining the titration curve, the volume of standard solution added may be plotted against the E. M. F. output of the chemical cell either expressed in volts or in pH units. A pH unit is defined as the logarithm of the reciprocal of the hydrogen ion concentration, and one pH unit corresponds to a change of approximately .059 volt. A neutral solution has a pH value of '7.

The present invention comprises means for determining the acidic or basic strength of a so lution of unknown concentration from E. M. F. determinations by automatically performing a titration and simultaneously recording E. M. F. output from a chemical cell as the titration is carried out. More specifically, the novel apparatus includes a chemical cell embodying titration electrodes, a recording instrument, a feed mechanism and control circuits constructed and arranged to coordinate the addition of standard solution from a graduated container to a measured volume of the solution of unknown strength and the recording of the resulting E. M. F. changes so that a smooth, accurate and directly usable titration curve is produced from which the strength of the solution of unknown concentration can be readily determined.

For purposes of ready understanding, the invention can be broken down into five portions as disclosed in Fig. 2, which, although cooperating with one another to produce a novel and improved result, may nevertheless be separately considered. The first of these portions is what may be termed the titration assemblage and includes the chemical cell and its electrodes. It is designated generally by the numeral IS. The second portion of the device which is directly connected to the titration electrodes may be termed a bridge circuit and is designated generally by the numeral 16. The third portion comprises the recording instrument and is denoted by the numeral [1. The fourth portion of the device which is generally designated l8 may be termed a relay circuit. And the fifth portion comprises the feed mechan sm which serves both to advance the chart in the recording instrument and to control the addition of standard solution. This fifth portion is denoted by the numeral l9.

Referring now to the drawings and to Figure 1 in particular, the exemplary form of the invention illustrated includes a main housing 29 having upper and lower sections Zila and b and disposed with n which are the recording instrument H, which includes a scale 2|, a pointer and pen 22. a chart 23, and the other component portions of the instant device. On the front face of the lower housing section 2% is a control panel 24 for the device, and upon which are centralized the controls for component circuit elements.

Titration assemblage Disposed adiacent the sides of the housing 2B are the titration assemblages 15. Two assemblages are provided which are independent of each other so that while one is being used in performing a titration the other can be prepared for the performance of another titration, thereby facilitating the running of a series of titrations. Each titration assemblage 15 includes a chemical cell setup comprising a beaker 25 in which the solution of unknown strength is placed, a calomel electrode 26 and a neutral indicator, or glass, electrode 21, both supported on a beaker cover 28, and a syringe 2t serving as a graduated container for the standard solution. Standard solution is supplied from the syringe into the posed between the electrodes 2% and 21.

4 beaker 25 by way of tubing 3% and 3| and a cook 32. Disposed atop the housing 21: is a flask 34 for reagent standard solution and the syringe 29 may be filled from it by way of a tube 34a, the cock 32 and the tube 3B.

To insure thorough mixing of the two so1utions as the titration is performed each assemblage is provided with a stirring motor 35 for driving an agitator 31, the latter being dis- Each motor 36 has a potentiometer 38 thereon whereby its speed can be controlled.

To support the stirring motor 3 5 and the chemical cell setup a stand 48 is provided which is rigidly secured to the housing 28. Adjacent the lower end of the stand and projecting laterally therefrom is a swingable arm 4! supporting on its end an adjustable platform 42 upon which the beaker 25 is placed. The beaker cover 28 together with the electrodes 2'5 and 21 supported therein is supported on a second arm 43 disposed intermediate the ends of the stand 40. The stirring motor 36 and its potentiometer 38 are attached to the stand by means of a third arm disposed adjacent the top of the stand 40.

The syringe 29 comprises two portions, a cylindrical body portion 29a and a plunger or piston portion 29b. The body portion 29a of the syringe is supported in a U-shaped spring clamp 45 secured directly to the side of the upper housing section 20a. The syringe plunger 2% is supported on a platform 46 which, in turn, is positioned atop a feed screw 48 for movement into and out of the cylindrical syringe body 2%.

Bridge circuit The bridge circuit l6 (Fig. 3) is provided to detect and adapt E. M. F. output of the chemical cells of the titration assemblages 15 for application to the recording instrument 57. It coznprises basically a push-pull, direct current amplifier having negative feedback for stabilization The titration electrodes 26 and 27 of each chemical cell are directly connected to pairs of input terminals 50, 5| and 52, 53 respectively, for the left and right titration assemblages l5, and a selector switch 54 is provided to alternatively connect these pairs of terminals to the bridge circuit.

Turning now to a detailed consideration of the circuit, two of its arms comprise a pair of identical vacuum tubes 55 and 56. As shown, each of the vacuum tubes has four elements, plates El and 58; screen grids 59 and 60; control grids 6i and 62; and cathodes 63 and 64, respectively, the screen grids and the cathodes of each being tied together. Vacuum tubes of the type known as type 38 have proven satisfactory. These tubes are operated at an extremely low plate voltage and with a filament voltage considerably lower than the rated value of the tube. This produces day to day uniformity of operation as well as long life.

By means of the switch 54 the E. M. F. output from the chemical cells is alternatively applied to the control grid 6| of the tube 55. The switch 54 actually connects either of the terminals 50 or 53, to which the indicator electrodes 21 are connected, to the control grid 6|, since, as hereinbefore set forth, the change in E. M. F. during titration is exactly equal to the change of potential of the indicator electrode. Thus,. the terminals 5| and 52 to which the calomel electrodes 2B are connected are grounded. For reference purposes, the control grid 62 of the tube 56 is grounded: simultaneously-with :the application ofchemicalcell output tothe grid of the tuba-55 by means of the-switch .54.

The vacuum tubesfit'andcfifi are linkedtogether by .a common resistor- 65 in-their cathode circuits. Because of this coupling, any change in the input voltage .to the grid 6! of the tube'55 changes the cathode bias of the tube 56. Asa result, the change in the plate current of the tube 5:5 is accompanied by a simultaneous change in the plate current .of the other tube 55 butin the opposite direction. Thus a differential voltage is developed across plate load resistors 6'! and 88 which comprise the other two arms of the bridge and appears at the output terminals 69;and 10 of the-bridge for application to the recording instrument i1.

Sensitivity and negative feedback forstabilization, arecontrolled by resistors 'H and 12 inserted between the common cathode resistor 65 and cathodes 63 and 6d of the vacuum tubes '55 and 56, respectively. It is particularly important in the titration of solutionsof extremely low acidic or basic strength thatthe device have high sensitivity. Using type 38 vacuum tubes operating at a plate voltage of 17.5 volts and witha filament voltage of 3.8 volts, it has been found that the requisite sensitivity is attained with resistance va ues of 7,000 ohms for the resistors H and 12 with approximately 50,000 ohms for the resistor 65.

As shown, the power supply for the bridge circuit includes a transformer M whose secondary supplies proper filament voltages and a voltage for application to a full wave'rectifier circuit. The rectifier circuit includes a double diode vacuum tube '15, a filter network which comprisesapair of capacitors 16 and Ti and a pair of resistors 18 and ill, and a voltage regulator'tube 86 whereby a constant output voltage is applied across an ordinary voltage divider network 80b. The voltage divider network 892) includes a potentiometer 80a from which the plate voltage for both of the vacuum tubes 55 and 56 in the bridge is tapped off.

While the pair of tubes id-and 5B are chosen to be of as nearly identical operating characteristics as possible, as a practical matter such identity is rarely found. Thus provisionis made to compensate for any difierences. To this end a voltage divider network comprising fixed resistors Si and 82 and a variable potentiometer 83 are provided in the filament circuits of'the tubes 55 and 56.

To compensate for variation of circuitoperating conditions so that a zero reading of the recording instrument ll obtains with no input to the grids E5! and 82, an adjustable plateload resistor '85 is provided'a portion :of which is in series with the plate load resistor 61 and "the other portion of which. is inseries with the plate load resistor 58. To'make this 'zero adjustment the switch M is moved to zero position which grounds the grids 6i and 62 of the vacuum tubes 55' and 56. The arm of the adjustable plate load resistor 85 is then moved until the plate voltage on both of the tubes ES-and 55 is equal. When such condition obtains there will be no output between the bridge output terminals 69 and i0 and thus the recording instrument ll will read zero. This adjustment, as with any instrument ofgthisgeneral type, must be made frequently and thus it .iS made a front panel adjustment controllable bya knob 85A on the controlpanel'M;

Similarly, a full scale adjustment .is pro- 6 :videdqso thatthe output fromthe bridge :circuit can 'be indicated over the entire range of the recording, instrument. To this end a variable resistor 86 whose movable arm constitutes a shunt is insertedin series with either the output terminal'69 or 10 of the bridge circuit, the shunt permitting of insertion of any portion of the resistor '86 in series with the output of the bridge,

This is also a front panel adjustment and is controlled by aknob 86A on the control panel 24. When-making such adjustment the switch 54 is operated to F. 8., or full scale position. Upon reference to Fig. 3 it will be seen that this grounds the grid 62 of the vacuum tube 56 and applies a reference voltage to the grid iii of the vacuum tube 55. This reference is obtained from the voltage divider network 801) and is on the order ofone volt.

Ordinarily in the performance of titrations by E. M. F. determinations the chemist is not par ticularly interested in the actual value of the E. ,M. F. output of the chemical cell, but rather he wants to know the change in output therefrom upon addition of standard solution to the solution of unknown concentration. Forcertain classes of work, however, the chemist might desire exact pI-l values,.p-articular1y when he desires to compare the acidic or basic strengths of more than one sample. The'provision of two titration assemblages inthe instant device permits of such comparison. However, .for that comparison to be accurate the output of the two chemical cells must becorrelated, and as a practical matter, there is some variation between calomel electrodes. So that a titration curve produced using one cell exactly corresponds to that produced using the other cell, provision is made to coinpensate for calomel electrode variation in order to :permit performance of comparison titrations by merely switching. between-the two assemblages l5 without necessity of application of some correction factor to the resulting curves before a comparisonthereof can be made. To this end, instead of grounding the grid 62 of the tube 56, a small reference voltage is applied by way of the switch 54 which is of a magnitude to compensate for differences of chemical cell output caused by calomel electrode variation. Thus, a balancing resistor network IE0 is provided by means of which the propercompensating voltage can be applied to the grid'62. This balancing network cornprises a pair of resistors It! and it? between which are a pair or" potentiometers it?) and Mi l connected in parallel and in parallel with an intermediate fixed resistor Edit. The movable armsof thepotentiorneters 503 and tile, which are independently adjustable, permit tapping off of reference voltages for application to the grid 52, the potentiometer Hi3 supplying the compem sating voltage for application to the grid 32 when using the right titration assemblage and the potentiometer 04 for supplying the compensating voltage to the grid 62 when using the left titration assemblage. The range of adjustment of these potentiometers is sufficient to permit application of reference voltages to compensate for a variation'between chemical cell outputs of 1 pH for either cell in either direction. These adjustments arecontrolled by knobs EMA and IMA on the control panel 24.

When the solution of unknown concentration is'acidi'c, with "a standard solution which is basic being added, the hydrogen ion concentration in the cell decreases and'the E. M. F. output of the cell increases. When .the solution of unknown concentration is basic with a standard solution which is acidic being added, the hydrogen ion concentration in the cell increases and the E. M. F. output of the cell decreases.

In the instance device the addition of standard solution is coordinated with the recording of E. M. F. output of the cell and the ordinates of the resulting plot correspond to the volume of standard solution added. The abscissae correspond to the E. M. F. output. Thus the ordinates are always of increasing value and in the case of a titration of an acid of unknown concentration with a standard base the abscissae increase as well. Thus a curve beginning on the left and ascending toward the right is obtained. But in the case of a titration of an unknown base with a standard acid the E. M. F. output of the cell decreases, in which case a curve beginning on the right and ascending toward the left is obtained. For the second case therefore the indication of the scale in the instrument may be considered as flopped over. The foregoing is accomplished in the instant device through the provision of a multiple stage switch H in the bridge circuit which has an operator knob Il0A on the control panel 24. As shown, the switch has six stages III-I I6 inclusive the first two of which namely, stages I I I and I I2 being effective to reverse the connections between the output terminals 69 and 10 of the bridge circuit I6 and the input terminals of the recording instrument II. These positions of the switch IIO are denoted on the control panel 24 by D, providing connection to produce a curve whose abscissae begin at the left and increase toward the right, and R for the reverse of the former connection. The stages H and H6 having corresponding R and D positions are both operative to connect the grid 62 of the tube 56 to ground, by way of the switch 54 for either the left or right positions of the latter. The stages H3 and H4 permit of application of a reference voltage, on the order of one volt in the present instance to the grid 6| of the vacuum tube 55 so that a full scale deflection of the recording instrument is attainable in either of the R or D settings of the switch IIO.

Recording instrument The recording instrument, a simplified diagram of which is shown in Figs. 2 and 4, comprises means to indicate and record the output E. M. F. of the bridge circuit It which is impressed upon it by maintaining a balance between the impressed E. M. F. and a self-contained M. F. source. It comprises a measuring circuit I23, which includes a source of E. M. F. such as a battery I2I and a resistance network designated generally I22, an amplifying circuit I24 and a balancing motor I 25 which are correlated to restore a balanced condition upon a change of impressed E. M. F. With a certain E. M. F. impressed and the resistance network I22 set to apply an equal but opposite E. M. F. from the battery I2I to balance it out, any change of E. M. F. impressed produces a condition of unbalance. This unbalance, appearing as a signal voltage between leads I23, is applied by way of the amplifying circuit I24 to the balancing motor I25 producing a rotation thereof in a direction determined by the direction of the unbalance. A mechanical connection between the balancing motor and an element of the resistance network I22 causes the effective resistance of the latter to be changed in follow-up action until a balance between the impressed E. M. F. and that from the cell I2I is restored.

The resistance network I22 includes fixed resistors I30, I3I, I32 and I33, and interposed between the resistors I30 and I3I is a slide wire unit I34 to which one of the output terminals 69 or I0 of the bridge circuit I6 is connected. The other bridge circuit terminal is unaffected by the resistance network. The output of the measuring circuit appearing between the conductors I23 is applied to the amplifying circuit by way of a converter I40 and an input transformer MI. The converter is merely a vibratory double-throw switch having a vibrator excited by the same A. 0. line that supplies one winding of the motor I25 and applies the output from the measuring circuit alternately to each of two halves of the primary winding of the input transformer I4I thus inducing an A. C. voltage in the secondary winding of the transformer. This A. C. voltage is amplified by the amplifyin circuit I24 and supplies the controlling power to the balancing motor I25 by way of a lead I26.

The balancing motor I 25 is a brushless, reversible variable speed induction motor which recognizes the phase of the driving power. One of the motor windings is continuously energized by the line voltage. The other winding is energized by the output from the amplifying circuit I24, with a current whose phase with respect to the line current determines the direction of rotation of the motor. Since the phase of the current of the output of the amplifier circuit I24 is di rectly determined by the direction of unbalance 0f the measuring circuit I20 the balancing motor pinion rotates in a direction determined by the unbalance. The contactor 0f the slide wire unit I34 in the measuring circuit I20 is mechanically connected to the motor pinion. Thus as the motor rotates, the contactor is moved altering the resistance of the measuring circuit resistance network I22 until a condition of balance between E. M. F. impressed and that from the battery I2! is restored, whereupon rotation of the balance motor ceases. With this system there is substantially no time delay between the actual unbalance and the beginning of the corrective action to restore a balanced condition. The pen and pointer 22 are also mechanically connected to the balancing motor pinion and thus it is moved simultaneously with movement of the contactor of the slide wire unit I34, and the amount of its movement is directly proportioned to the amount of impressed E. M. F.

It will be obvious to one skilled in the art that the range of measurement of the recording instrument I1 may be varied by substituting different values for the fixed resistors I30, I3I, and I32 in the measuring circuit resistance network I22. While the actual resistor substitution arrangement is not shown in the drawings, any desired provision can be made under the control of a range selector switch I45 to change the values of each of these resistors. The switch M5 is disposed centrally of the control panel 24.

Chart and syringe feed mechanism An important feature of the present invention resides in the means illustrated in Figs. 6 and 7 to simultaneously advance the chart of the recording instrument I? and add standard solution from the syringe 29 of the titration assemblage I5. Stated generally, this means comprises a feed motor I50 together with suitable shafts, gearing and feed screws, the operation of which is controlled by the relay circuit I8 and coordinated with the operation of the recording instrument I! acecgeer 9 so that addition of standard solution takes} place only when a balanced condition'in the-recording instrument obtains.

The motor I56 has included withinits housing a speed reduction gear system (not shown) from which a drive shaft I 5i extends and theouter end of which is coupled to a transverse-shaft I52. The latter is journaled in 'bearingsIS l" and I55 in a gear shift assembly, designated generally I56. Considering first thechart drive, on the end of the transverse-shaft I52 oppositetne motor I50 is fashioned a worm I58, which'isin continuous-engagement with a worm gear iii which, in turn, isiast on a vertical shaft I69.- The upper end of'the vertical shaft Ifiii supports abevel gear IGI which is incontin-uous engagementwith a driven bevel gear IEZ-suppOrtedadjacent. the end of a stub shaft I63. The stub shaft I63. is drivinglyconnected, by means of a spring. biased, toothed coupling I64, to a horizontal shaft I65 upon which is mounted a roll I65 for the. chart 23.

The gear shift assembly I56 permits alternative feeding of the syringes 29 of the two titration assemblages It. simultaneously with the advance of: the chart 23. To this end, the assembly I56 includes abevel gear IIiBsupported intermediate theends .of the transverse shaft I52, together with a pair of. bevel gears I69 and H splined' tocoaxially aligned shafts Ill and I12, respec-- tively; to rotate the same, the gears I68 and. I?!) being shiftable axiallyof the shafts III'I and I12 into and out of engagement with the driving gear- I68. The outer ends of the shafts Ill? and Ill support bevel gears IE3 which mesh with'bevel gearsv I'M supported. on. the feed screws 48-;

Each of ,the, syringe feed screws i3 is oftelescoping construction comprisinginner and outer threaded elements I75 and I'I6.. The bevel gear I'M is rigidly secured on the outerthreaded element H6 and thus causes it .to rotate. Fixed-to the upper end :of the element Iltzis a disengageable nut I78. The inner threaded element passes through the nut I73, and when the nut is engaged the inner element I15 is fed upwardly through it. Thus, the syringe plunger 2% is forced upwardlyintothe cylindrical body 29a of the syringe and thereby forces solution from it.

When it is desired to refill the syringe simultaneously with the lowering of the .feed screw, thenut I'I8is disengaged releasing theinner feed screw element I15; The syringe plunger 29bis loaded with lead shot or the like to give it con siderable weight. Thus, upon release .ofthe nut- I18 its weight will force it downwardlyandicause: the inner feed screw. element I15 to be pushed downwardly at the same time. Prior to releasingthe disengageable nut, the cockv 32 isv operated to connect the syringe 29 to the reagent flask 3d atop the housing 2E3. Thus, as the plunger moves downwardly, reagent solutionis drawn into the syringe.

To limit upward movement of the feed screw, a limit switch I19 is provided which isact-uated. by an operator I'IBa fixed adjacent the lower end of the inner feed screw element I'lE. This switch is in series with the line supplying power to operate the feed motor I50 and when it is actuated upon contact by the operator I'I9a it interrupts further feed.

A solenoid I80 is utilized to produce shifting of the gear assembly I55, that is to say, to alternatively bring the bevel gears I69 and I'Ill' into and out of mesh with the driving bevel gear I68.- To this end,: the,solenoidjscoupledto a 7 standard solution; To this end the supply voltage yoke I82 which is laterally shiftable in the assembly I56. The arms of the yoke I82 are forked and are received in peripheral grooves I 83 in the hub portions of the bevel gears its and HE. Upon energization of the solenoid ltd, the yoke I82 is shifted toward the right as viewed in Figs. 6 and '7 and the bevel gear Ilil is brought into engagement with the driving bevel gear I38 whereupon the left titration assemblage is operated. When thesolenoid I is de-energized a spiral spring I85 supported between the yoke Iiiii and theframe of the assembly I56 which was compressed upon energization of the solenoid becomes operative to shift the assembly I56 so that the bevel gear I63 is brought into engagement with the driving bevel gear I58 whereupon the titration assemblage on the right side of the instant apparatus i made operative.

Upon reference to Fig. 3, it will be seen that the solenoid IIlil is actuated by line voltage and the switch controlling its energization is mechanically connected to the switch 55 and controlled by the knob 54A on the control panel 2d.

Relay circuit The operation of the chart and syringe feed mechanism is controlled by the relay circuit I8 which, in turn, is controlled by the operation of the recording instrument II. The relay circuit I8 includes a normally closed relay Iiil and atripping circuit I92 therefor constructed and arranged so that the feed motor IiiIi is tie-energized as long as any voltage unbalance exists andas long as there is any movement of the balancing motor I25 and its associated points However when balance is achieved and the motor I25 comes to rest, the motor [59 is actuated to continue the addition of standard solution to the solution of unknown concentration and advance the chart 23.

Thetripping circuit ISZ comprises a pair of vacuum tubes I93 and its both of which may be included in the same envelope. The vacuum tube I83 comprises simply a diode rectifier which, in combination, with a voltage regulator tube I and a filter network I56 supplies power for the tube I94.

The circuit for the tube I9 3 is constructed so that the tube I9 1 is normally non-conducting. When an unbalance of the recording instrument is produced, a signal voltage is app-lied to the control grid oftthe tube its directly from the same lead I26. from the amplifying circuit I2 4 in the recording instrument I"! that energizes the control winding of the balancing motor I25. This signal causes the tube I96 to become conducting. The output from the tube I94 is fed to the relay I93 to energize the same, whereupon it operates to interrupt the line supply voltage to the motor I58 thus stopping it and preventing further addition of standard solution and advance of the chart 23; A brake (not shown) may be used to prevent the motor from overrunning and causing.

additional standard solution to be added. When a balanced condition is restored in the recording instrument I1 and there accordingly is no signal voltage applied to the control grid of the tube I94, the tube again become non-conducting permitting the relay I95) to close whereupon the motor I Ellis-again actuated to continue the addition of standard solution and the advance of the chart 23;

Provision is made to vary the speed of the motor I50 to control the rate of addition of to the motor is controlled by means of a variable transformer I09 which may be of the familiar type known as a variac. The operation of this transformer is made a front panel adjustment and is controlled by a knob I99A disposed adjacent the control panel 24.

Operation While the operation of the instant device will be clear from the foregoing to one skilled in the art, it will be helpful to review it briefly. Assuming identity of operating conditions of the balanced circuit components and that a sufficient warm-up period has been allowed, the first step is to apply a standard potential to the control grids BI and 62 of the tubes 55 and 56 in the bridge circuit I6 to make a full scale adjustment. This is done by turning the switch 54 to the F. S. position and then adjusting the potentiometer 86 so that the pointer 22 of the recording instrument ll reaches a suitable upper scale limit.

Having thus established a full scale adjustment, the switch 54 is moved to zero position whereupon the control grids of both the bridge tubes 55 and 56 are grounded so that there will be no output from the bridge circuit I B. The zero control potentiometer 85 is then moved to balance the plate voltage applied across the bridge arms. When a balance is attained the pointer 22 of the recording instrument I! indi-- cates a zero scale reading. Since the zero and full scale adjustments are interrelated it will be necessary to repeat the foregoing steps until absolute adjustment obtains, two or three times usually being sufiicient.

Now assume that the right titration assemblage I5 of the device has been prepared to perform a titration. This entails filling the syringe 29 With standard solution and placing the beaker 25 containing a known quantity of the solution of unknown concentration in position with the electrodes 26 and 21 placed therein. The next step is to operate the switch 54 of the bridge circuits It to R position thereby applying the E. M. F. output of the chemical cell of the right titration assemblage I5 to the grid of the tube 55 and correspondingly grounding the grid of the tube 56.

With the bridge circuit thus set up, the feed motor I50 is started so that standard solution from the syringe 29 is added to the solution of unknown concentration in the beaker 25 and the chart 23 of the recording instrument I! is correspondingly advanced. It should be immediately observed whether the pointer tends to move in the proper direction as hereinbefore noted. Should the pointer tend to go in the wrong direction, the feed should be stopped and the switch H moved from either R to D positions or vice versa as the case may be.

Having again started the feed motor I50 to proceed with the titration, standard solution is added drop by drop to the solution of unknown concentration. The E. M. F. output of the chemical cell accordingly changes, is detected by the bridge circuit I and is impressed on the recording instrument I! producing an unbalance of the measuring circuit I thereof. This automatically results in the operation of the balancing motor I to restore a balanced condition and in stopping the feed motor I50 simultaneously. While the balancing motor I25 begins to operate, moving both the pointer and the contactor of the slide wire unit I34 in the measuring circuit, the feed motor I50 which drives boththe syringe and the chart is stopped by the action of the relay circuit I8. When a balanced condition of the measuring circuit I20 is attained, the chart and syringe motor starts up as permitted by the action of the relay circuit and thus more standard solution is added. This is a continuous process completely under the control of the device itself and requires no attention from an operator until the curve recorded on the chart 23 is complete. Actually, the steps, addition of standard solution, production of unbalance, interruption of the addition of standard solution and advance of the chart, restoration of balance, and resumption of addition of standard solution and advance of the chart, are so minute that a smooth curve is produced which is directly usable since there is substantially no time delay between the actual unbalance and the beginnin of action to restore a balanced condition. The curve is exceedingly accurate because the condition of balance must be attained before a single drop of standard solution is added with a corresponding amount of chart movement.

While the apparatus is performing the titration utilizing the titration assemblage [5 on the right side thereof, the operator is free toprepare the left titration assemblage. Upon so doing, and upon completion of the right titration, the switch 54 in the bridge circuit is moved to "L position and the foregoing sequence is followed for this titration just as Was the case for the titration using the right titration assemblage.

When it is desired to perform a series of comparison titrations and more particularly when results plotted in pH values against quantity of standard solution added are desired, the necessary correlation between the two chemical cells of the titration assemblages can be attained (to compensate for variation between the calomel electrodes 26) by operating the switch 0 to pl-I position and making the necessary adjustments of the potentiometers I03 and I04 with no input to the grid SI of the tube 55. This adjustment having been made, the titrations proceed just as before following the same sequence and the resulting curves can be used directly without necessity of application of any correction factor to compensate for chemical cell differences.

From the foregoing, therefore, it can be seen that a titration apparatus constructed in accordance with the present invention is effective to accurately and automatically perform a titration and simultaneously plot a titration curve as determined by the E. M. F. output from a chemical cell involving a solution of unknown concentration. The resulting curve is smooth and directly usable not only for determining the equivalence point in a single titration but are also directly usable for comparison of titrations of several sample solutions of unknown concentration without the necessity for the use of any correction factor.

We claim as our invention:

1. In a recording titration device provided with a chemical cell adapted to contain a quantity of test specimen having electrodes positioned therein between which the E. M. F. of the cell is produced, supply means for introducing standard solution into said cell, and recording means provided with a movable chart and recording stylus comprising in combination, a normally balanced electrical network, means for impressing the cells E. M. F. upon said normally balanced network to produce therein a condition of voltage unbalance, a first driving means for moving said recording stylus and for simultaneously rebalancing said electrical network, a second driving means for simultaneously feeding standard solution from said supply means into said chemical cell and for advancing said movable chart, and a control circuit rendered operative in response to the voltage unbalance of said network for disabling the operation of said second driving means during operation of said first driving means.

2. In a recording titration device provided with a chemical cell adapted to contain a quantity of test specimen having electrodes positioned therein between which the E. M. F. of the cell is produced, supply means for introducing standard solution into said cell, and recording means provided with a movable chart and recording stylus comprising in combination, a measuring circuit upon which the cells E. M. F. is impressed comprising a variable resistance network and a selfcontained source of E. M. F. which serve to detect an unbalance E. M. F. between the cells E. M. F. and the self-contained source of E. M. F., a first driving means for moving said recording stylu]s and for simultaneously adjusting said variable resistance network to balance the cells E. M. F. and the self-contained source of E. M. F., a second driving means for simultaneously feeding standard solution from said supply means into said chemical cell and for advancing said movable chart, and a control circuit responsive to said unbalance E. M. F. for selectively disabling the operation of one of said driving means during operation of said other driving means.

3. In a recording titration device provided with a chemical cell adapted to contain a quantity of test specimen having electrodes positioned therein between which the E. M. F. of the cell is produced, supply means for introducing standard solution into said cell, and recording means provided with a movable chart and recording stylus comprising in combination, circuit means upon which the cells E. M. F. is impressed comprising a variable resistance network and a self-contained source of E. M. F. which serve to detect an unbalance E. M. F. between the cells E. M. F. and the self-contained source of E. M. F., a motor connected to move said recording stylus and simultaneously to adjust said variable resistance network to balance the cells E. M. F. and the self-contained source of E. M. F., an energizing circuit for said motor controlled by the unbalance E. M. F. detected by the said circuit means, a drive for simultaneously feeding standard solution from said supply means into said chemical cell and for advancing said movable chart, and a circuit energized in response to said unbalance E. M. F. for interrupting the operation of said drive when said motor is energized to move said recording stylus and simultaneously to adjust said variable resistance network.

HAROLD A. ROBINSON. ROLLIN H. BRIGGS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,530,833 Keeler Mar. 24, 1925 1,684,645 Smith et a1 Sept. 18, 1928 2,376,311 Hood May 15, 1945 2,392,916 Gruss Jan. 15, 1946 2,396,934 Wallace Mar. 19, 1946 2,400,828 Keinath May 21, 1946 2,423,480 Caldwell July 8, 1947 2,452,587 McCoy Nov. 2, 1948 2,464,708 Moseley Mar. 15, 1949 FOREIGN PATENTS Number Country Date 715,397 Germany Dec. 20, 1941 OTHER REFERENCES Canadian Chemistry and Metallurgy, September 1931, Automatic Controls in the Chemical Industry (pages 239, 240, 245 and 246).

Lingane, Ind. and Eng. Chem. Anal. Ed, vol. 20, April 1948, pages 285-292.

Kolthoff and Furman, Potentiometric Titrations," 2nd Ed., pages 112-143. John Wiley and Sons, 1931.

Barredo and Taylor, The Electrochemical Society, Preprint 92-96, October 15-18, 1947, pages 303-310.

Robinson, The Electrochemical Society, Preprint 92-38, October 15-18, 1947, pages 503-522.

Hickman et al., Ind. and Eng. Chem. Anal. Ed., vol. 5, 1933, pages -68.

Shenk et al., Ind. and Eng. Chem. Anal. Ed, vol. 7, 1935, pages 194-197. 

1. IN A RECORDING TITRATION DEVICE PROVIDED WITH A CHEMICAL CELL ADAPTED TO CONTAIN A QUANTITY OF TEST SPECIMEN HAVING ELECTRODES POSITIONED THEREIN BETWEEN WHICH THE E. M. F. OF THE CELL IS PRODUCED, SUPPLY MEANS FOR INTRODUCING STANDARD SOLUTION INTO SAID CELL, AND RECORDING MEANS PROVIDED WITH A MOVABLE CHART AND RECORDING STYLUS COMPRISING IN COMBINATION, A NORMALLY BALANCED ELECTRICAL NETWORK, MEANS FOR IMPRESSING THE CELL E. M. F. UPON SAID NORMALLY BALANCED NETWORK TO PRODUCE THEREIN A CONDITION OF VOLTAGE UNBALANCE, A FIRST DRIVING MEANS FOR MOVING SAID RECORDING STYLUS AND FOR SIMULTANEOUSLY REBALANCING SAID ELECTRICAL NETWORK, A SECOND DRIVING MEANS FOR SIMULTANEOUSLY FEEDING STANDARD SOLUTION FROM SAID SUPPLY MEANS INTO SAID CHEMICAL CELL AND FOR ADVANCING SAID MOVABLE CHART, AND A CONTROL CIRCUIT RENDERED OPERATIVE IN RESPONSE TO THE VOLTAGE UNBALANCE OF SAID NETWORK FOR DISABLING THE OPERATION OF SAID SECOND DRIVING MEANS DURING OPERATION OF SAID FIRST DRIVING MEANS. 